By Linda Givetash, Laura Saravia and Abigail Williams
Iran has for the first time acknowledged the existence of an open case involving a former FBI agent who vanished more than a decade ago.
In a filing to the United Nations, Iran said the case involving Robert Levinson was "on going," but did not elaborate.
"According to the last statement of Tehran's Justice Department, Mr. Robert Alan Levinson has an on going case in the Public Prosecution and Revolutionary Court of Tehran," said a filing to the U.N.'s Working Group on Enforced or Involuntary Disappearances obtained by NBC News Saturday.
Levinson's family confirmed Iran had told both the U.N. and their lawyer it has an open case "about our husband and father."
"We welcome Iran’s taking the first step to finally end this nightmare. Now it is time to send him home to us," the family said in a statement to NBC News Saturday.
But on Sunday, Iran said the case doesn't involve criminal charges and "was just a file about a missing person."
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The case was opened on "the basis of goodwill and humanitarian issues," Foreign Ministry spokesman Abbas Mousavi said at a news conference broadcast on the state-run Press TV.
"It is normal that a case is opened like it's done for any missing people anywhere in Iran," Mousavi added.
A Trump administration official in a statement to NBC News described Iran's past efforts in the Levinson case "as nothing short of a sham."
"Iran’s continued suggestion they are conducting an investigation can be described at best as half-hearted and has been part of the larger deception campaign that Iran has employed regarding Mr. Levinson for more than 12 years," the administration official said.
"If Iran’s leadership want to prove us wrong, Iran should turn over any and all information related to its investigation of Mr. Levinson to his family, the Swiss, or the United Nations, who can evaluate whether or not they have accurately characterized their 'action'."
The developments come amid a renewed push to resolve the case and growing tension between Washington and Tehran.
The U.S. is now offering up to $25 million for information about Levinson after the Trump administration issued an increased reward last week.
Levinson, who suffers from diabetes, was last seen in March 2007 on Kish Island off Iran's coast.
His family said if there were any charges against Levinson, after years missing without contact, he had "paid whatever penalty."
"We want to see him, and we want to know what are the charges? If there are charges," the family said in the statement Saturday.
Levinson wasn't included in a 2016 prisoner exchange with the U.S. and Iran. At the time, U.S. officials said they were unable to confirm where Levinson was despite repeatedly raising the issue with Iranian officials.
Iran had denied any knowledge of Levinson and previously offered to help search for him.
Rumors have circulated for years about his fate but Levinson has not been heard from since 2011, when family members released photos and videos they had been sent in which he begged for help.
"I have been held here for three and a half years," he said in the video. "I am not in very good health. I am running very quickly out of diabetes medicine."
No trace of Levinson has shown up since.
Linda Givetash is a London-based freelance journalist.
Laura Saravia is a producer based in London.
Abigail Williams is a producer in the NBC News Washington bureau.